Windshield wiper drive device

ABSTRACT

A windshield wiper drive device for driving a windshield wiper ( 11 ) in an alternating motion in a range of motion ( 17 ) between two turning point positions (A, C) includes a motor ( 1 ) for moving the windshield wiper ( 11 ), a detector ( 6 ) for detecting a time at which the windshield wiper ( 11 ) moves past a given position (A, C) in the range of motion ( 17 ), a control circuit ( 8 ) for reversing the direction of motion of the motor ( 1 ) at each turning point position (B, D), and an incremental transducer for detecting the distance traveled by the windshield wiper ( 11 ) from the given position (A, C). The control circuit ( 8 ) reverses the direction of motion of the motor ( 1 ) as soon as it is detected that the windshield wiper ( 11 ) has traveled a defined distance.

[0001] The invention relates to a windshield wiper drive device havingthe characteristics recited in the preamble to claim 1.

PRIOR ART

[0002] For a long time, windshield wiper drive devices have been knownin which a rotary motion of a motor that rotates in a predetermineddirection is converted into a reciprocating motion of the windshieldwiper by means of an eccentric mechanism. Recently, windshield wiperdrive devices in which the drive motor is controlled directly indifferent directions of rotation as a function of the reciprocatingmotion of the wiper have increasingly been introduced as well. In suchdrive devices, it is necessary to detect positions of the windshieldwiper, at least at the turning points of its motion, so that thedirection of rotation of the motor can be reversed at the correct time.Conventional drive devices use separate detectors for the variouspositions for this purpose, or else a single detector is used to detecta plurality of detectands, in other words objects of arbitrary type thatcan be detected by a detector; each detectand corresponds to oneposition to be detected.

[0003] This type of position detection for controlling the windshieldwiper drive device is complicated and accordingly expensive. For thisreason, windshield wiper drive devices of this type have until now beenused primarily in motor vehicles in the upper price class, even thoughthey have advantages that would make it desirable to use them morebroadly. Specifically, while in drive devices with an eccentricmechanism the range of motion of the windshield wiper is predeterminedby the eccentric mechanism, and accordingly a redesign of the drivedevice is needed for every vehicle model with a different range ofmotion, in a drive device with a reversing motor, it suffices to changethe positions of a detector or a detectand, in order to thereby adaptthe range of motion of the windshield wiper to the given conditions ofeach individual vehicle model. This flexibility of windshield wiperdrive devices with a reversing motor moreover makes them especially wellsuited for use in windshield wiper systems with a recessed parkingposition.

ADVANTAGES OF THE INVENTION

[0004] The windshield wiper drive device of claim 1 is distinguished byits simple and flexible layout, which enables economical manufacture ofthe drive device and thus its use even in less-expensive vehicle models,and which also makes it simpler to adapt the windshield wiper drivedevice to the given conditions of arbitrary models of vehicles.According to the invention, it in fact suffices to detect merely asingle given point of the range of motion of the windshield wiperdirectly with a detector; from this point, the sideways motion of thewindshield wiper can be measured relatively with the aid of anincremental transducer, which in principle makes it possible to detectan arbitrary number of positions of the windshield wiper using adetector. The location of the turning points of the windshield wiper isdefined by their distance from the point of the range of motion detectedby the detector. How great this distance should be in one or the otherdirection of motion of the windshield wiper can be specified to thecontrol circuit to suit, depending on the circumstances in which thewindshield wiper drive device is used.

[0005] Especially if only two positions of the windshield wiper, namelythe turning point positions, have to be detected, then the simplestoption is for the defined distance from the given position to theturning point position to be the same for both directions of motion.

[0006] In an especially preferred further refinement of the invention,the control circuit includes a delay element, in order to reverse thedirection of motion of the motor also whenever a certain time haselapsed since the passage of the windshield wiper through the givenposition. Specifically, if the motion of the windshield wiper is blockedby some obstacle, such as snow that has slid off the windshield, or thelike, and for this reason the windshield wiper can no longer reach itsturning point position, then in this further refinement the controlcircuit can reverse the direction of motion of the motor even before theactual turning point position is reached and can thus maintain wiperoperation over a more limited range of motion. The delay element can beoperative either for both directions of motion of the windshield wiperor selectively for only one of the two directions.

[0007] In a further preferred embodiment, it is provided that thedetector, between a first of the two turning point positions of thewindshield wiper and the given position, detects a signal having a firstvalue that originates at a detectand, and detects a second value betweenthe given position and the second turning point position. As a result,it is possible for the control circuit, when the windshield wiper drivedevice is turned on, to decide by calling up the signal value detectedby the detector which side of the given position the windshield wiper islocated on, and to select its initial direction of motion accordingly.The direction of motion is expediently selected such that the windshieldwiper moves toward the given position, so that upon the passage throughthe position, the detector detects a change in the signal, on the basisof which the measurement of the relative travel distance measurement canbe initialized with the aid of the incremental transducer.

[0008] Preferably, the detector and the detectand execute a motionrelative to one another that is coupled to the motion of the windshieldwiper. To that end, the detectand will mainly be secured to a mechanismthat follows the reciprocating motion of the windshield wiper, whileconversely the detector is stationary.

[0009] Various different designs of the detector and detectand arepossible. For instance, the detector can be a magnetic field sensor,such as a Hall sensor, and the detectand can be a magnet pole whosefield interacts with the magnetic field sensor. Alternatively, a wipercontact as the detector and a conductive surface connected to a givenpotential as the detectand, or a photodetector as the detector and awindow in an opaque surface or an opaque region on a transparentsubstrate as the detectand can be considered.

[0010] To realize a windshield wiper parking function in the windshieldwiper drive device of the invention, the control circuit is preferablyequipped with a turn-off function; when the turn-off function isactivated, the control circuit does not reverse the direction of motionof the motor when the windshield wiper has reached the first turningpoint position, but instead turns off the motor when the windshieldwiper has reached an extreme position located on the far side of thisturning point position.

[0011] This extreme position can, just like the turning points, beascertained by using the incremental transducer to track the distancetraversed by the windshield wiper from the given point.

[0012] Alternatively, it is possible to design the detectand in such away that the signal detected by the detector at the extreme positionchanges over from the first to the second value. In that case, thereaching of the extreme position can also be determined directly withthe aid of the detector.

[0013] In a further refinement, it is provided that an auxiliarydetectand adjoins the detectand on the far side of the extreme position.This auxiliary detectand will never be detected by the detector duringnormal operation of the windshield wiper drive device; but if it isdetected, this is an indication that an error has occurred in thecoupling of the relative motion of the detector and the detectand to themotion of the windshield wiper, for instance because the windshieldwiper has not been secured to its shaft in the correct position, so thatthe error has to be corrected to enable error-free operation of thewindshield wiper.

[0014] Depending on the operative principle of the detector, theauxiliary detectand may for instance be a succession of alternatingmagnet poles, which in their motion in the detection range of thedetector lead to a rapidly alternating signal, or a conductive surfaceconnected to a second potential, or a partly transparent surface.

[0015] Further characteristics and advantages of the invention will become apparent from the ensuing description of exemplary embodiments,taken in conjunction with the drawings.

DRAWINGS

[0016] Shown are:

[0017]FIG. 1, part of a windshield wiper drive device of the invention;

[0018]FIG. 2, a section taken along the line II-II of FIG. 1;

[0019]FIG. 3, the part shown in FIG. 1, in a second embodiment of theinvention;

[0020]FIG. 4, a section taken along the line IV-IV of FIG. 3;

[0021]FIG. 5, the detector and the detectand of the present invention indifferent phases of the cycle of motion of the windshield wiper;

[0022]FIG. 6, the course over time of individual signals of significancefor controlling the windshield wiper drive device;

[0023]FIG. 7, the course over time of signals relevant for the control,in accordance with a further-refined embodiment of the invention;

[0024]FIG. 8, the detector and detectand in the presence of an obstacleon the window to be washed by the windshield wiper;

[0025]FIG. 9, the detector and detectand in a recessed position; and

[0026]FIG. 10, a detectand with an auxiliary detectand.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0027]FIG. 2, in a side view in fragmentary section, shows a motor 1 ofa windshield wiper drive device of the invention and a reducing gearconnected to it. The reducing gear includes a worm 2, which is securedon the shaft of the motor, and a worm wheel 3 driven by the worm 2. Anincremental transducer 19 detects the rotation of the worm 2 and outputsa fixed number n of pulses per revolution of the worm to a controlcircuit 8 (see FIG. 2). Depending on the polarity of the supply voltagesof the motor, which are applied to two supply terminals 10 (only one ofwhich is visible in the drawing), the motor drives the worm wheel 3either clockwise or counterclockwise. FIG. 2 shows the worm wheel 3 in asection taken along its axis, in the plane marked II-II in FIG. 1. Theworm wheel is solidly connected to a drive shaft 4, which transmits thereciprocating motion of the worm wheel 3 to a windshield wiper (notshown).

[0028] The worm 2 and worm wheel 3 are accommodated in the same housing7. A Hall sensor 6 is mounted in an opening of the housing 7, as seenparticularly in FIG. 2. Opposite the Hall sensor 6, a magnet 5 is letinto the worm wheel 3. The magnet is oriented such that the field axisextends parallel to the axis of the drive shaft 4, so that over thecourse of motion of the worm wheel 3, the same pole of the magnet 5always faces toward the Hall sensor 6. The Hall sensor 6 and the magnet5 are shown in FIG. 1 as outlines drawn with dashed lines, since in theperspective view of FIG. 1 the Hall sensor 6 is concealed by the wormwheel 3 and is therefore not actually visible, and the magnet 5 islocated on the side of the worm wheel 3 away from the observer. The Hallsensor 6 outputs two different signal levels to a control circuit 8depending on whether the magnet 5 is opposite it or not. From the changein the signal level of the Hall sensor 6, the control circuit detectsthat the windshield wiper has reached a given point along its path, atwhich point one edge of the magnet 5 is just then sweeping past the Hallsensor 6, as shown in the drawing. The details of this detection will bedescribed further hereinafter.

[0029]FIGS. 3 and 4 show a second embodiment of the motor and reducinggear of a windshield wiper drive device of the invention. Elements thathave already been described in conjunction with the embodiment of FIGS.1 and 2 are identified by the same reference numerals and will not bedescribed again.

[0030] In this second embodiment, the worm wheel has a sector-shapedcutout 15. This worm wheel is admittedly incapable of executing acomplete revolution of 3600, but this is not a problem, since thewindshield wiper, driven by way of the worm wheel 13 and the drive shaft4 does not execute a complete revolution, either. In this embodiment,instead of a Hall sensor, a photodetector 16 is provided, such as aphotodiode. On a side of the housing 7 opposite the photodiode, a lightsource 14, such as a light-emitting diode or LED, is let in. When thecut-out sector 15 is located between the light source 14 and thephotodetector 16, the photodetector detects the projected light admittedby the sensor 15 and outputs a signal at a first value to the controlcircuit 8. If the worm wheel 13 is located between the light source 14and the photodetector 16, then only very little light reaches thephotodetector, and as a result a second signal level is output. Wheneverthe windshield wiper passes a given position along its path, whichcorresponds to the position in FIG. 3 of the worm wheel 3 or its cut-outsector 15 relative to the photodetector 16, the signal output by thephotodetector 16 to the control circuit 8 changes its value, whichenables the control circuit 8 to ascertain that the windshield wiper ispassing the given positions.

[0031] It is understood that there are still other options besides thetwo described above for detecting the passage of the windshield wiperthrough the given position; for instance, the sector cutout 15 could bereplaced with a slit in the worm wheel that extends over a suitableradius in the circumferential direction; the worm wheel could besubstantially transparent and could be opaque only in the region of thecorresponding sector, etc. Also, instead of the circumferentiallyelongated magnet 5 or the sector 15, a magnet without any significantlength in the circumferential direction or a radial slit could be used;then the control circuit 8 would not have to detect the passage of thewindshield wiper through the given position from a change in the signalbut instead from the fact that the signal temporarily assumes adifferent value.

[0032] The mode of operation of the windshield wiper drive device of theinvention will now be described in further detail in conjunction withFIG. 5: In FIG. 5, parts A, B, C, D indicate the position of the magnet5 and the Hall sensor in the embodiment of FIGS. 1 and 2 as well as theassociated position of a windshield wiper 11 in four different stages ofits motion, which will hereinafter be called the A, B, C and Dpositions, corresponding to those parts of the drawing in which they areshown.

[0033] In part A, the windshield wiper 11 and the magnet 5 coupled to itmove counterclockwise, and the magnet 5 is just now beginning to overlapwith the Hall detector 6. The signal S (see FIG. 6) output by the Halldetector changes from 0 to a first value.

[0034] At the same time, the control circuit begins to add up countingpulses that are furnished by the incremental transducer 19. The resultof the counting is shown in FIG. 6 as signal d. The signal d increases,until in the B position of the windshield wiper and the magnet, itattains a limit value d_(max). As soon as this limit value d_(max) isreached, the control circuit changes the polarity of the drive voltageU_(mot) for the motor that it outputs via supply lines 9 (see FIGS. 2,4), in order to reverse the direction of rotation of the motor and thusthe direction of motion of the windshield wiper 11. Accordingly, the Bposition corresponds to the lower turning point position of thewindshield wiper.

[0035] In its motion in the opposite direction, the magnet and thewindshield wiper reach the position shown in part C, in which the magnet5 is just now leaving the detection range of the detector 6. At thisinstant, the signal S drops back to 0, as can be seen in FIG. 6. Onceagain the control circuit begins to add up counting pulses of theincremental transducer 19 and thus generates signal d that increases instairstep fashion. After a certain distance traversed, the signal dreaches its limit value d_(max) in the position D, whereupon the motordriving voltage U_(mot) again changes its sign. The windshield wiper nowbegins to move counterclockwise again and thus once again reaches theposition shown at A, whereupon the cycle repeats.

[0036] As one can easily see, the location of the turning pointpositions of the windshield wiper motion is not predetermined by theconstruction of the drive mechanism; instead, it can be determined in asimple way by a suitable choice of the threshold value d_(max) or by achoice of different threshold values for the two turning pointpositions. The drive device of the invention can thus easily be adaptedto use in vehicle models with different-sized ranges of windshield wipermotion.

[0037]FIG. 7 shows the mode of operation of a further-refined embodimentof a windshield wiper drive device of the invention in terms of thecourse over time of the signal S of the Hall sensor 6; the value dx,formed by the control circuit 8; the distance traversed since the givenpoint by the windshield wiper; a time delay value t, and the supplyvoltage output by the control circuit 8 to the motor 1 via the supplylines 9. This further-refined embodiment is distinguished from thatdescribed in conjunction with FIGS. 5 and 6 in that in it, the controlcircuit additionally includes a clock generator and a counter forcounting the pulses output by the clock generator. The counted value ofthese pulses is the signal t shown in FIG. 7.

[0038]FIG. 7 first shows a normal operating cycle of the drive device,with phases A1, B1, C1, D1 that correspond to the A, B, C, D shown inFIG. 5 for the magnet and the Hall sensor or windshield wiper. Thecontrol circuit counts pulses of the incremental transducer 19 until thecounted value d reaches a threshold value d_(max). This is the case ateach of the turning point positions B1 and D1.

[0039] In the second cycle shown, having the phases A2, E2, C2, D2, anobstacle 12 has formed on the window to be cleaned by the windshieldwiper 11, such as a relatively large amount of snow on the lower end ofthe wiping region, as schematically indicated in the right-hand part ofFIG. 8. The left-hand part of FIG. 8 shows the corresponding position,marked E, of the magnet 5 and the Hall sensor 6; the entire range ofmotion of the magnet is represented as an outline 17 drawn with dashedlines.

[0040] The windshield wiper still passes normally through position A(phase A2), and the control circuit thus begins to count the pulses ofthe transducer 19; initially, the signal d increases. Simultaneouslywith the passage of the windshield wiper through the given position inphase A2, the control circuit begins to count the value t upward. In thefirst cycle shown, t was reset to 0 each time (in phases B1 and D1) whend reached the limit value d_(max). In the second cycle, d does not reachthe limit value d_(max), because the windshield wiper has remained stuckin the position E shown in FIG. 8. The counting process thereforecontinues until t attains a limit value t_(max), and thereupon t and dare reset to 0. At the same time, the sign of the motor drive voltageU_(mot) is reversed, and the drive motor changes its direction ofrotation. In phase C2, the windshield wiper again passes through thegiven point, at which the signal S of the Hall sensor 6 changes itsvalue. From there, the wiping motion proceeds normally, until the wiperis blocked a second time.

[0041]FIG. 9 shows the magnet 5 and the Hall sensor 6 and the windshieldwiper 11 in a different further-refined embodiment of a windshield wiperdrive device of the invention, in a position marked F, in which thewindshield wiper 11 is located outside the range of motion 17represented by the outline drawn with dashed lines. This position isassumed by the windshield wiper 11 whenever the windshield wiper is notneeded. To allow this position F to be approached, it is provided in thefurther-refined windshield wiper drive device that the driver, when heactuates a switch to turn off the windshield wiper, sets a turn-offfunction of the control circuit 8 in motion. When the turn-off functionis activated, the control circuit 8 no longer monitors whether thesignal d is exceeding its limit value d_(max) immediately followingphase A. Thus the direction of the motor 1 is no longer reversed whenthe windshield wiper reaches the position B corresponding to phase B.Instead, the windshield wiper moves onward until such time as the magnet5 has almost passed the Hall sensor 6, and the signal S of the Hallsensor 6 is beginning to drop again. If this is the case, the controlcircuit 8 turns the motor 1 off. Thus in this embodiment, the bottomedge of the magnet 5, in terms of FIG. 9, is utilized to mark the givenposition A, C in the range of motion of the windshield wiper. From theother, upper edge of the magnet 5 in terms of the drawing, the reachingof the recessed position F of the windshield wiper is detected.

[0042] Alternatively, upon activation of the turn-off function, thelimit value d_(max), which corresponds to the position of the windshieldwiper at the turning point position B, can be replaced by a higher limitvalue. In that case, the windshield wiper 11 moves on until reaching theposition defined by the increased limit value, and when this position isreached the control circuit turns off the motor.

[0043] Turning off the ignition of a vehicle can lead to a situation inwhich the power supply to the motor is interrupted while the wiper islocated at some arbitrary point between the turning point positions Band D, so that the wiper comes to a stop on the window. To assure insuch a case that the windshield wiper will restart correctly when theignition is turned on again, the control circuit determines the value ofthe signal S when the windshield wiper drive device is started. If thissignal has reached the first value, then the windshield wiper is locatedeither at the turning point position B or between that position and thegiven position A or C. In that case, the control circuit 8 selects thepolarity of the supply voltage of the motor such that the motor startsup in the direction of the turning point position D, regardless of thedirection in which the windshield wiper was moving before it was turnedoff. If conversely, from the value of the signal S, the control circuitlearns that the wiper is located between positions A, C and D, then itdrives the motor in the direction of position B. In this way, regardlessof the starting position of the windshield wiper, the control circuit isinitialized by a passage through the position A, C, so that it cancorrectly evaluate the counting pulses of the incremental transducer 19.

[0044]FIG. 10 shows a magnet 5, a Hall sensor 6, and auxiliary magnets18 in a variant of the embodiment described in conjunction with FIG. 9.Just as in FIG. 9, the magnet 5 and the Hall sensor 6 are shown in theposition F. The magnets 18 are disposed, each with alternating polarity,adjoining the edge of the magnet 6 that marks the recessed position ofthe windshield wiper. If the windshield wiper drive device is correctlyadjusted, then the auxiliary magnets 18 are never detected by the Hallsensor 6. At most, they can be detected if the position of the magnet 5,which is movable in common with the windshield wiper 11, has beenincorrectly changed relative to the Hall sensor 6 in the course ofrepair or maintenance of the windshield wiper drive device. In such acase, it can happen that some of the auxiliary magnets, whose size isshown exaggerated in the direction of motion in comparison to that ofthe magnet 5, will move along ahead of the sensor 6 and thus cause arapid alternation in the signal S. From this signal S, which fluctuatestoo fast in comparison with the distance actually traversed and reportedby the incremental transducer, the control circuit can tell that theauxiliary magnets are being detected by the Hall sensor 6 and cancorrect the incorrect position, optionally automatically, or can causean error report to be issued so that the problem can be quickly takencare of.

[0045] The present invention has been described here with a focus onmagnets and a Hall sensor for detecting the position of the windshieldwiper, but it is understood that the concept of the invention is notlimited to a specific combination of detector and detectand. On thecontrary, from the teaching provided above, it is readily possible forone skilled in the art to employ optical, electromechanical, or othermeans for the position detection.

1. A windshield wiper drive device for driving a windshield wiper (11)in an alternating motion in a range of motion (17) between two turningpoint positions (B, D), having a motor (1) for moving the windshieldwiper (11), a detector (6) for detecting a time at which the windshieldwiper (11) moves past a given position (A, C) in the range of motion(17), a control circuit (8) for reversing the direction of motion of themotor (1) at each turning point position (B, D), characterized in thatthe windshield wiper drive device includes an incremental transducer(19) for detecting the distance traveled by the windshield wiper (11)from the given position (A, C); and that the control circuit (8)reverses the direction of motion of the motor (1) as soon as it isdetected that the windshield wiper (11) has traveled a defined distance.2. The windshield wiper drive device of claim 1, characterized in thatthe defined distance is the same for both directions of motion.
 3. Thewindshield wiper drive device of one of the foregoing claims,characterized in that the control circuit (8) includes a delay element,in order to reverse the direction of motion of the motor (1) as well, ifa certain time t_(max) has elapsed since the passage of the windshieldwiper (11) through the given position (A, C).
 4. The windshield wiperdrive device of one of the foregoing claims, characterized in that thedetector (6), between a first turning point position (B) and the givenposition (A, C), detects a signal having a first value that originatesat a detectand (5), and detects a second value between the givenposition (A, C) and the second turning point position (D).
 5. Thewindshield wiper drive device of claim 4, characterized in that thecontrol circuit (8) upon being turned on selects the direction of motionof the motor (1) as a function of the value of the signal (S) detectedby the detector (6).
 6. The windshield wiper drive device of claim 4 or5, characterized in that the detector (6) and the detectand (5) executea motion relative to one another that is coupled to the motion of thewindshield wiper (11).
 7. The windshield wiper drive device of one ofclaims 4-6, characterized in that the detector and the detectand are amagnetic field sensor (6) and a pole, associated with it, of a magnet(5), or a wiper contact and a conductive surface connected to a givenpotential, or a photodetector (16) and a window (15) in an opaquesurface (13) or an opaque region on a transparent substrate.
 8. Thewindshield wiper drive device of one of the foregoing claims,characterized in that the control circuit (8) has a turn-off function,and the control circuit (8), when the turn-off function is activated,does not reverse the direction of motion of the motor (1) when thewindshield wiper (11) has reached the first turning point position (B)but instead turns off the motor when the windshield wiper has reached anextreme position (F) located on the far side of this turning pointposition (B).
 9. The windshield wiper drive device of claim 8,characterized in that the detectand (5) is designed such that at theextreme position (F), the signal (S) detected by the detector (6)changes over from the first value to the second value.
 10. Thewindshield wiper drive device of claim 8 or 9 and claim 4, characterizedby an auxiliary detectand (18), which adjoins the detectand on the farside of the extreme position (F), and whose detection by the detector(6) is an indication of an error in the coupling of the relative motionof the detector (6) and the detectand (15) to the motion of thewindshield wiper (11).
 11. The windshield wiper drive device of claim 10and claim 7, characterized in that the auxiliary detectand is asuccession of alternating magnet poles (18), or a conductive surfaceconnected to a second potential, or a partially transparent surface.